Safety device for a press comprising stroke terminating means



R. G. SAFETY DEVICE FOR A PRESS COMPRISING March 5, 1957 ERICSON ETAL 2,783,838

STROKE TERMINATING MEANS Filed Jan. 13, 1955 iim InI/Qn tors Roy 6 Erz'cson Fran/r E Strazzon United States Patent SAFETY DEVICE non A PRESS COMPRISING STROKE TERMINATING MEANS Roy G. Ericson, Danvers, and Frank E. Stratton, Beverly,

Mass., assignors to United Shoe Machinery Corporation, Flemington, N. .l., a corporation of New Jersey Application January 13, 1955, Serial No. 481,683

8 Claims. (Cl. 164-23) This invention relates to improvements in cutting presses and more particularly to improvements in cutting presses of the type known as clicking machines commonly used for cutting blanks from sheet material, which improvements are directed to the end of reducing the possibility :of injury to the operator.

Clicking machines, as heretofore constructed, comprise a cutting support, a beam or platen mounted upon a spindle at one side of the support for swinging movement across it and power means for reciprocating the beam toward and away from the support to force a freely movable cutting die through sheet material on the support. In such machines it has been common to provide manually operated control means for the power means arranged so that, upon actuation of the manual control means, the power means are controlled to reciprocate the beam through a stroke of predetermined length. Means are also commonly provided for adjusting the length of the stroke and for varying the uppermost position of the beam in its cycle of operation in order to accommodate dies of dilfer'ent heights.

'In'United States patent application Serial No. 409,670, filed February 11, 1954, in the names of Frank Seabury II and Robert W. Bradley, there is disclosed and claimed an improved clicking machine having a platen and a work support each'comprisirig a conductive member, the two members being insulated from each other. In the operation of this machine, the cutting stroke is initiated by the downward movement of a control handle after which an electronic control means is arranged to cause the power means to terminate the downward movement of the platen in response to the reduction of the electrical resistan'ce' between said members below a, predetermined value, for example, by the formation of a low resistance electric circuit therebetween through the cutting die.

Many advantages are realized by the use of this stroke terminating control. For example, the wear of the work support is reduced, and the necessity for adjusting the rest position of the platen to accommodate different dies or lengthsof cuttingstroke is obviated. Further a certain me'asureof safety is provided in that, should an operators finger chance to be interposed directly between the members during a stroke in the absence of a die, and Work piece, the stroke will be automatically terminatedby reduction of the inter-member resistance to the critical value by the conductance of the finger before severe injury occurs. However, if theinter-member conductance path should beiinterrupted', as where-the'finger rests ona'work piece or on faidie resting-one work piece, such protection is no longer'efiectivei Accordingly, it is an important object of the present invention to provide animproved cutting press organization of the type disclosed in the'above application wherein the-operator is protected from injury in the event that the platen member-engages, in the course of a cutting stroke, a portion of-theoperatonsuch as a finger, even where-insulative materialintervenes between the portion and the support member.

7 2,783,838 "[Pattma Mar. 5, 17957 a "ice To this end and in accordance with a feature of the I by the formation of a conductance path.

Other features and advantages of the invention will be best understood from the following description takenin connection with-the accompanying drawings in which,

Fig. l is a diagrammatical representation-of apparatus embodying the present invention; and v Fig. 2 is a side view partly in section and on an en larged scale of a portion of another embodiment of the present invention showing modified electrode arrangements.

Referring to Fig. l, the cutting press organization illustrated therein comprises a work support 10 including a conductive work support member 12, which may consist of conductive rubber, for supporting work pieces 14 of sheet material such as leather, fabric or the like to be operated upon by a freely movable die 16 to produce blanks. A- platen or beam 18, including an insulated metallic striking plate 19 providing a conductive platen member, is mounted upon a vertical spindle 20 at one side of the support for swinging movement across the support 10 and is arranged for reciprocation toward and awayfrom the support to force the die 16 through the work piece.

Power means for reciprocating the platen 18 are preferably hydraulic and are illustrated in Fig. 1 as comprising a piston 22 connected to the lower end of .the spindle 20 and slidably mounted in a cylinder 24.

- Control of the fluid operated motor is provided by a valve 26 having an axially movable valve element-28. When the valve element 28 is in its upper position as shown, a lower port 30 in the cylinder 24 is connected to a supplypipe 32 and an upper port 34 is connected to an exhaust pipe 36 so that the piston 22 is urged upwardly. When the valve element 28 is in its lowermost position, the connections to the ports are reversed so that the piston is urged downwardly. Thevalve element 28 is normally biased upwardly by a spring 38 so that the normal or rest position of the platen is relatively elevated. A sole-' noid' 40 is arranged by connection of its armature to the valve element 28 to move the element into its lowermost position when the solenoid is energized.

Manually operable means for controlling the fluid operated motor to initiate a downward stroke of the platen 18 comprises a switch 42 which as shown in Fig. l i may be disposed at the front of the platen, and an opergting handle 44 of conductive material. The handle 44 is I the other of the shoulders of the'reduced portion48 at the upper and lower-limits of travel'of the handle. The

handle is normally biased in. its upward position by -a spring 52 but may be readily moved downwardly so that a camming surface 54 formed thereon will engage and move rearwardly the plunger of the switch 42 to close its pleted through thesaid frame.

The energizing circuit for the solenoid 40 may be In Fig. 1, the handle 44 is connected to the greases traced from one line terminal 56 through the switch 42, through the solenoid'40 and'thr'ough the normally closed contacts '58 of arelay'switcn'saand tiack'tdthe other line terminal 62. Accordingly, it will be seen that downward movement of the handle 44 causes the solenoid 40 tobe energized to move tli valve element 28'to initiate thecutting stroke'of the platen. 2

Electronic means for terminating the cutting stroke in response to reduction of the resistance between the strik; ing plate 19 and the conductivework'support member below 'a' predetermined value comprises the relay 60 and the control circuit therefor including a thyratron 64 whichhas the solenoid of the relay 60 in its anode circuit. The thyratron is normally biased nonconductive from asource which comprises the secondary v66 of a transformer 68 conneeted in a half-wave rectifier circuit with a rectifier and RC filter elements 72 and 74. The positive side of'the biassupply is connected to the thyr atron cathode while the negative side is connected to the thyratron' grid through a resistor 76 and a conventional grid-circuit limiting resistor 73. Anode current is supplied by a second half-wave rectified circuit powered by the windingofi of the transformer but. having a separate rectifier 80 and an output condenser 82. From the positive terminal of the anode supply, the energizing circuit proceeds to the anode through the normally open contacts 84 of a relay 86 connected to be energized when the switch 42 is closed, a resistor 38 and the solenoid of relay 60. This solenoid is shunted by a condenser bank 90 having a selector switch 92 by which the capacitance shunted across the solenoid may be varied. The negative terminal of the anode supply is connected to the cathode of the thyratron.

It will be seen that if the input terminals of the thyratron stroke terminating control are connected one to the cathode and the other to the junction between the resistors 76 and 78, the voltage of the grid bias supply, namely that across, the condenser 74, willbe divided between the resistor 76- and the resistance across the input terminals as. a voltage divider. Accordingly, the actual grid bias will vary substantially in proportion to the resistance across the input terminals. One of the input terminals is connected to the striking plate 19 while the other. is connected to the conductive work support member 12 and itwill be seen that when the striking plate forces a die through a work piece and into contact with the work support member, the bias voltage will be reduced to a very low. value causing the thyratron to fire and to cause therelay 60 to open the contacts 58 after a delay interval determined by the capacitance value selected by the switch 92, This of course has the effect of deenergizing the solenoid 40 to terminate the stroke.

In accordance with a feature of the invention, means are provided for electrically connecting the operator with the conductive work support member 12 during. the cuttingystroke of the machine. This means comprises the metal handle 44, which is electrically connected with the work support member 12 as described above. In order for the operator to initiate the cutting stroke of the platen 18, he must grasp with one hand the handle 44 and move' it downwardly to close the switch 42. If during the stroke and while the operator is grasping the handle 44 with one hand, the striking plate 19 should engage his other hand, the body conductance of the operator will be connected across the input terminals of the thyratron relay so that if the resistor 75- represents a suflicient pro portionof the total resistance of the voltage divider network comprising resistor 76 and the bodyresistance of the operator, the grid bias will drop. to the firing potential. Toinsure stability of the normal eut-ofi condition of the thy'ratron 64, the bias voltage provided is a few volts above theirated cut-off voltage. The value of the resistor 76- employed should be sutficientlylow to avoid termina tion of the stroke before completion of the out under normal conditions. Except in the most unusual conditions of operation such as those involving the cutting of material of low resistivity, the critical input resistance may be established at a value su' fii c'iently high so that even under unfavorable conditions of contact of the operator with the handle 44, the resistance between the handle and the striking plate 19 (and hence the intermember resistance) will be reduced below the critical value where the operator is grasping the handle with one hand and the other hand is engaged by the striking plate. We have found a satisfactory value for the critical input resistance to be about 680,000 ohms for the general cutting of upper leather. 'i v I i It will be understood in Fig. 1 that the connections between the input terminals of the stroke terminating control and the support and platen members may be reversed if desired.

Another arrangement of the elements of a cutting press organization which is comprehended by the present invention is illustrated in Fig. 2. In this arrangement the cop duetive work sup un'member 12"" is" insulated from the bed 10 by a barrier layer. of insulative material while the platen member, comprising the s triking plate 1?; is' electrically connected to'thc 'frame" of the: platen 1e and to the frame of the n'iachine. metal handle 44 11 is insulated from the platen by bushings 101 but iis connected electrically mine support member 12 by the indicated lead 102 to provide'an'electrode for connecting the operator with the work support member 12 during a cutting stroke.

The time occupied by a cutting stroke of the machine is sufiicie'ntly short, being in the order of one second, to make remote the likelihood of the operator disengaging his hand from the handle 44 during th edownward move} ment of the beam. Accordingly, if desired, the switch 42 may be arranged to actuate a holding relay having two sets of normally open contacts, en set being used to Connor theeiijer'g'ization erase solenoid 40' while the other,

se'tis: arranged in 'alioldfng circuit. With this arrange; ment, the relay 60 should have a second pair of normally closed contacts in the above holding circuit. Other arrangements for connecting" the operator to the support member during normal operation of. the press may com: prise a conductive that as use with conductive shoes, Wiist bands, 'eftcl', bufvfe pr'efer for convenience to employ' the handl'as shown. c

'In operation, the valve element 28 is initia lly.supported in its npper'mmtpmamH by the spring 38 so that. the fluid o erated motor holds theplaten 18 in its uppermost position, The dpe'rat'or may then position a work piece 14 on the work support member 12 position a die 16 on the work piece, and. move the handle M down to initiate the cutting stroke of the machine. Ifat any time during the cutting stroke the striking, plate 19 should touch any part of the body'of the operator, the thyratron 64 will; fire to terminate the cutting stroke within the number. of thousandths of a second selected; by positioning the switch 92 which number'is determined by the particular cutting conditions. The operation of the embodiment shown in Figf2'co'rresponds with the operation of the emb diment ofFig'. 1. i

Having thus describedour invention, what we claim as new and desire to secure by. Letters Patent of the" United States is:

1. In a cutting press, a frame supporting a conductive work support member, a platenincluding, a conductive a s. m m r s a e m. aid support member. said 1 3 sia S PPQIWQ or Sa 'f ame or movem nt Or. ward and away from said support member andarranged so that the platen member is adapted; upon such movement. toward; the support member to engage a die. and press it through a work piece on said support member, pen/yerv means for moving said platen,- control means for? said power means, said control means operating nor mally to retain said; plated in; a sens s whe ein an; platen and support members" arm; a predetermined maximum separation, said control means including stroke initiating means operable to cause said power means to move said platen toward said support member and also stroke terminating means responsive to reduction of the inter-member resistance below a predetermined value to effect termination of such movement, and means other than the conductive support member operable in the normal operation of the press to connect the operator to the support member, whereby contact of an exposed portion of the operators body with the platen member during a cutting stroke is operable to reduce the inter-member resistance for efiecting termination of the stroke.

2. In a cutting press, a work support including a conductive work support member, a platen including a conductive platen member insulated from said support memher, said platen being supported for movement toward and away from said support to cause the platen member to engage a die and press it through a work piece on said support and into contact with said support member, power means for moving said platen, control means for said power means, said control means including stroke initiating means comprising a conductive handle electrically connected to the work support member and movable to cause said power means to move said platen toward said support, and stroke terminating means operative in response to reduction of the electrical resistance between said members below a predetermined value to effect termination of such movement.

3. In a cutting press, in combination, a work support including a conductive work support member, a platen including a conductive striking plate insulated from the remainder of the platen, said platen being supported for movement toward and away from said support to cause the striking plate to engage a die and press it through a work piece on said support and into electrical contact with said support member, power means for moving said platen toward said work support, control means for said power means, said control means including stroke initiating means operable to cause said power means to move .said platen toward said support and also stroke terminating means operative in response to reduction of the resistance between the plate and the support member below a predetermined value to effect termination of such movement, and means other than the conductive support member operable in the normal operation of the press to connect the operator to the support member, whereby contact of an exposed portion of the operators body with the striking plate during a cutting stroke is operable to reduce said resistance for efiecting termination of the stroke.

4. In a cutting press, a work support including a conductive work support member, a platen including a conductive striking plate insulated from said support member, said platen being supported from movement toward and away from said support, said platen being adapted upon movement toward said support to engage a die and press it through a work piece on said support member, power means for moving said platen, a conductive element, control means for said power means, said control means including stroke initiating means operable by movement of said conductive element to cause said power means to move said platen toward said support, and also stroke terminating means operable in response to reduction of the resistance between the plate and the support member below a predetermined value to effect termination of such movement, and electrode means including said element connected to said conductive support member and adapted for connecting the operator to the work support member during such movement of the platen.

5. In a cutting press, in combination, a work support including a conductive support member, a platen including a conductive platen member insulated from said support member, said platen being supported for movement toward and away from said support to engage a die and press it through a work piece on said support member, power means for moving said platen, control means including stroke initiating means operable to cause said power means to move said platen toward said support and also stroke terminating means responsive to reduction of the resistance between said members below about 500,000 ohms to etfect termination of such movement, and means other than the conductive support memher operable in the normal operation of the press to con nect the operator to the support member, whereby contact of an exposed portion of the operators body with the platen member during a cutting stroke is operable to reduce the inter-member resistance for effecting termination of the stroke.

6. In a machine for operating on work pieces, said machine having power driven work piece treating means representing a potential hazard to a body portion of the operator, a conductive surface associated with said treating means to engage said portion in an area of hazard, an electric relay having two input conductors, said relay being responsive to reduction in the resistance between said conductors provided by human body conductivity to eflect a switching operation, means for connecting one input conductor to said conductive surface, electrode means operative in the normal course of operation of the machine to connect the body of the operator to the other input conductor, and means controlled by said relay and operative to modify the operationof said machine to prevent injury to the operator upon engagement of the said portion of the operators body with the conductive surface.

7. In a press, a work support, a platen movable in a path toward and away from said work support, said platen having a conductive lower surface, power means for moving said platen in said path, means for controlling said power means to initiate movement of said platen toward said support, an automatically operating modifying control for said power means. said control including two input conductors and being responsive to the reduction in the resistance between said two conductors afforded by the conductivity of a human body portion connecting said conductors for causing said power means to terminate the movement of said platen toward said support, means for connecting one of said conductors to the conductive surface of the platen, and means operative in the normal operation of the press for connecting the body of the operator to the other input conductor.

8. In a press, pair of presser members mounted for relative movement toward and away from each other, at least one of said members having a conductive surface subject to being touched by the operator during said relative movement of the presser members, motor means for effecting said relative movement of said presser members, control means operable to cause said motor means to effect relative movement of said members toward one another, an electrode adapted to be connected to the operator in the normal course of operation of the press, and a control electrically connected to said electrode and to said conductive surface and operatively connected to said motor means for controlling it to interrupt the relative movement of the presser members toward one another in response to the operators touching said conductive surface while connected to said electrode.

No references cited. 

